Effects of Mn doping on structural properties and conduction mechanism of NaCu0.2Fe0.8−xMnxO2 (x = 0.4; 0.5; 0.6; 0.7) materials

The NaCu0.2Fe0.8−xMnxO2 (x = 0.4; 0.5; 0.6; 0.7) samples were synthesized using conventional solid states method. Analyzing the DXR measurement through the use of FullProf allowed us to prove the purity of these samples and to corroborate that they crystallize in hexagonal system in the R-3 m space group. The refinement of the crystalline structure revealed the O3 structure type for compounds whose x = 0.4 and x = 0.5 and the P3 structure type for compounds whose x = 0.6 and x = 0.7. It is to be noted that the impedance spectroscopy results expressed in terms of a Nyquist diagram demonstrated three contributions which are grain, grain boundary and electrode effects. The conduction mechanism deduced from the study of ac conductivity goes in good agreement with the overlapping large polaron (OLPT) to compounds whose x = 0.4 and 0.5. However, for the sample whose x = 0.6 and 0.7, the conduction process was determined through the correlated barrier hopping (CBH) model. Furthermore, we examined the influence of Mn substitution on structural and electrical properties. Therefore, by increasing the Mn amount, we inferred that the structure changed from O3 to P3, which affected the electrical properties and enhanced the grain conductivity owing to the decreasing volume of the sodium site.